1. Field of the Invention
The present invention relates to a thermal infrared sensor device and a thermal infrared sensor array.
2. Description of the Background Art
As an example of a conventional thermal infrared sensor device, Japanese Patent Laying-Open No. 2003-207391 proposes a technique to reduce effective reflectivity and improve infrared absorption efficiency by forming a three-dimensional structure having dimensions in micrometers, as described in paragraphs [0011]–[0012] and shown in FIG. 1(a) and (b). As another example, Japanese Patent Laying-Open No. 7-190854 proposes, in paragraph [0007], a thermal infrared sensor device allowing incident infrared light to be reflected multiple times within a concave portion serving as a detecting portion to improve infrared absorption efficiency substantially. These thermal infrared sensor devices are fabricated by bulk micromachining, a process for forming a concave portion in a surface of a silicon substrate.
Further, for example, Japanese Patent No. 3062627 proposes a technique in which a reflecting layer 18 is formed on an upper surface of a substrate and an absorber coating layer 23 is formed thereon, as described on page 2, right column, line 44 to page 3, left column, line 27 and shown in FIG. 1, to thereby enhance infrared absorption efficiency, as described on page 4, left column, lines 11–15 and shown in FIG. 3. High infrared absorption efficiency is also achieved by a technique proposed for example in U.S. Pat. No. 6,667,479 to provide a reflector layer 34A below a detection structure 24 having a detection layer 28 therein, as described in column 2, lines 14 through 23 and shown in FIG. 1. In these techniques, a thermal infrared sensor device is fabricated by surface micromachining, a process for providing a structure on an upper surface of a substrate by processing a sacrificial layer formed on the substrate.
Such a conventional thermal infrared sensor device as described above requires a complex structure to obtain high absorption efficiency. Since the thermal infrared sensor device has a complicated structure and a large film thickness of the order of micrometers, heat capacity of the entire thermal infrared sensor device has become increased. To achieve a thermal infrared sensor device with higher performance, however, it is necessary to improve heat insulation properties and to convert received infrared radiation (heat rays) to a greater change in temperature. To maintain good responsiveness while improving heat insulation properties, the thermal infrared sensor device should have smaller heat capacity as a whole.
The conventional thermal infrared sensor device formed by surface micromachining can achieve high infrared absorption efficiency without requiring a complex structure. The device, however, requires a special material for its fabrication, and thus it has a problem with productivity.
On the other hand, U.S. Pat. No. 6,576,556 proposes, in FIGS. 1–7, a diode infrared sensor device which can be fabricated by bulk-surface composite micromachining, a combination of bulk micromachining and surface micromachining. The publication's FIGS. 1–7 show a manufacturing process, of which FIG. 7 shows a completed device. This infrared sensor device achieves high infrared absorption efficiency. Furthermore, Japanese Patent Laying-Open No. 2000-321125 shows in FIG. 1 a structure in which a detecting portion is provided with a reflecting layer 10 for improved properties. However, the structure in Japanese Patent Laying-Open No. 2000-321125 has greater heat capacity than that of the structure provided by U.S. Pat. No. 6,576,556, and thus it has a problem with deterioration in responsiveness.